KR20110084201A - A ethylene cracking furnace - Google Patents

Abstract

The invention comprises a high pressure steam drum (1), a convection section (2), a radiation section, several furnace tubes (14) installed perpendicular to the radiation section, a burner (5), and a quench boiler (60). As an ethylene cracking furnace; Each furnace tube of the radiation section comprises one first stroke pipe 7, one second stroke pipe 8 and one connecting member 9, wherein the dismantling material passes through the inlet of the first stroke pipe. Supplied, discharged through the outlet of the second stroke pipe; The first stroke pipe 7 and the second stroke pipe 8 are non-dividing furnace tubes, the center line of each furnace tube being in the same plane; The connecting member (9) is a three-dimensional structure comprising an inlet bend (10), a return bend (11) and an outlet bend (12); The inlet bend 10 and the outlet bend 12 are located on both sides of the plane passing through the centerlines of the first stroke pipe 7 and the second stroke pipe 8; The lateral projection of the connecting member 9 is one symmetrical continuous infinite curve, and the inner diameter of the furnace tube relates to an ethylene cracking furnace which is changed one or more times along the longitudinal direction of the furnace tube.

Description

Ethylene Digestion Furnace {A ETHYLENE CRACKING FURNACE}

The present invention relates generally to the petrochemical industry, and more particularly to the tube structure of ethylene cracking furnaces used in the petrochemical industry.

The cracking furnace is an important device of the ethylene plant. Radiant coils in ethylene cracking are important factors in determining cracking selectivity, increasing olefin yield in the pyrolysis product and flexibility for various feedstocks. Improving the structure and arrangement of the radiant coil is the most important part for the technical development of tubular cracking furnaces. In recent decades, single-row split diameter-variable tubular, mixed-row split diameter-variable tubular, unsplit diameter-variable tubular, single-pass equal-diameter Several arrangements with various structures have been proposed, including tubular and the like.

The arrangement of the furnace tubes has been developed from the original single-row method to the double row method. As for the single-row mode, more floor space is required for the same production capacity, but the advantage is that the temperature distribution around the furnace tube is uniform and there is little obscure phenomenon; With regard to the double heat mode, it is possible to substantially reduce the bottom space of the cracking furnace, but the unclear phenomenon is very serious and thus the temperature distribution around the furnace tube is negatively affected.

Lummus Crest Inc. (USA), in Chinese patent CN1067669, is a furnace installation with six first-pass tubes and one second-pass tube, wherein the first tube passes through a manifold conduit at the lower end through a second-pass. The equipment connected to the tube was disclosed. Since this structure has six first-pass tubes and one second-pass tube, when the furnace tube receives heat and expands, the second-pass tube first expands downward, and the first-pass tube first. Moves downward due to the traction of the second-pass tube, the first-pass tube further away from the second-pass tube receives less force, and the first-pass tube closer to the second-pass tube Will receive more power. In addition, since the upper and lower manifold conduits are firmly connected, the expansion difference between the second-pass tube and the first-pass tube can only be adjusted by a balance system disposed at the inlet of the first-pass tube, As a result, the furnace tube will bend when the first-pass tube cannot move with the second-pass tube.

Exxon Chemical Patents Inc. (United States) disclosed a facility in Chinese patent CN1259981 and another in US patent US6528027. A common disadvantage of the arrangement of the two radiation tubes is that as the lower part the first-pass tube is inclined outwards, but the second-pass tube is not inclined in the opposite direction, and the adjacent first-pass tube is inclined to the other side, As a result, when the radiation tube is subjected to heat, the overall radiation coil will not be able to maintain a single heat and will naturally exhibit two heat to relieve stress. As a result, the heating of the radiation tube is not uniform, and thus there will be a temperature difference between both sides of the radiation tube wall, and the furnace tube will bend towards the burner because the temperature on the side adjacent to the burner is high and the temperature on the opposite side is low.

Patent document EP1146105 discloses a cracking furnace with a tube arrangement of the following kind: a two-pass radiation coil is arranged perpendicular to the firebox of the radiation section, the first-pass tube and the second-pass tube. The straight tube portion of is arranged in a common plane, the first-pass straight tube and the second-pass tube are connected to the curved tube through the "S" shaped tube, respectively, the first-pass tube and the second-pass The "S" shaped tubes of the tubes are each parallel, and the shape of the curved tube to which they are connected can be semicircular, semi-elliptical or semi-oval, with an angle to the plane containing the straight tube portions formed by each curved tube. Is the same. This kind of tube arrangement overcomes the disadvantages of the radiant tube structure described above. However, the 2-1 type furnace tube has a "Y" tube at the lower part of the "2-tube section" of the first-pass tube, so that two tubes connected to the "Y" tube have a heating path of the radiation tube. The bending of the tubes still exists because they differ with respect to the resulting expansion.

In reviewing the prior art described above, it can be seen that none of the various conventional radiation tube arrangements can avoid tube deformation or bending and displacement. In addition, such deformation or bending causes the heating of the radiation tube to be uneven, thus the radiation tube will be further deformed and displaced. The heat absorptivity is thus limited and the life of the radiation tube in the cracking furnace is shortened.

It is an object of the present invention to solve the problems of the prior art by providing an ethylene cracking furnace with a two-pass radiation coil, which can ensure uniform heating, good mechanical performance and extended service life.

This object is achieved by the following technical solution.

An ethylene cracker comprising a high pressure steam drum, a convection section, a radiation section, a plurality of groups of radiation coils, a burner and a transfer line exchanger arranged perpendicularly to the combustion chamber of the radiation section, each of which comprises A first pass tube, a second pass tube, and a connection member connecting the first pass tube and the second pass tube; A feedstock is introduced into the inlet end of the first-pass tube and flows out of the outlet end of the second-pass tube; The first-pass tube and the second-pass tube are undivided radiation tubes, the centerline of each radiation tube being in a common plane; The connecting member is a three-dimensional structural member comprising an inlet bending tube, a return bending tube and an outlet bending tube; Each first-pass tube is connected to an end of the inlet bending tube at the bottom end of the first-pass tube remote to the inlet end of the first-pass tube, The other end is connected to an end of the return bending tube, the other end of the return bending tube is connected to an end of the outlet bending tube, and the other end of the outlet bending tube is a second-pass tube. Is connected to the bottom end of the second-pass tube that is far from the outlet end of the second pass tube; The inlet bending tube and the outlet bending tube are respectively arranged on two sides of a plane which receives the centerlines of the first-pass tube and the second-pass tube; The plane formed by the centerline of the group of inlet bending tubes intersects (viewed from the side) the plane formed by the centerline of the group of outlet bending tubes, and the intersecting line is the first-pass tube. And the two planes which are in a plane for receiving the centerline of the second-pass tube, the two planes defined by the centerlines of the inlet bending tube and the outlet bending tube are centerlines of the first-pass tube and the second-pass tube. Symmetrical about the plane that receives it; The return bending tubes connecting the inlet bending tube of the group and the outlet bending tube of the group are parallel to each other, and their projections on the plan view are straight lines with the same length; The projection of each connecting member on the side view is the same curve which is symmetrical, continuous and closed,

In order to meet the requirement of lowering the temperature and reducing the pressure drop during the decomposition process while maintaining the heat absorption invariant, the radiation coils can be arranged in a diameter-varying manner. For different requirements, the diameter-variable arrangement can be realized by many alternatives, including but not limited to the alternatives listed below, in each alternative wherein the first-pass tube and the second The length of the pass tube is the same:

(1) The inner diameter of the first-pass tube is the same as the inner diameter of the connecting member, and the inner diameter of the second-pass tube is different from the inner diameter of the first-pass tube and the connecting member, and the second The inner diameter of the pass tube is greater than the inner diameter of the first-pass tube and the connecting member, this alternative may be referred to as "one-time diameter-variable";

(2) The inner diameter of the first-pass tube is the same as the inner diameter of the connecting member, and the inner diameter of the lower portion of the second-pass tube is the same as the inner diameter of the first-pass tube and the connecting member, The inner diameter of the upper portion of the second pass tube is greater than the inner diameter of the lower portion of the second pass tube, and this alternative may be referred to as "double diameter-variable";

(3) the inner diameter of the first-pass tube is equal, the inner diameter of the connecting member is larger than the inner diameter of the first-pass tube, and the inner diameter of the second-pass tube is the same as the inner diameter of the connecting member;

(4) The inner diameter of the first-pass tube is equal, the inner diameter of the connecting member is larger than the inner diameter of the first-pass tube, and the inner diameter of the lower portion of the second pass tube is equal to the inner diameter of the connecting member. The same, wherein the inner diameter of the upper portion of the second pass tube is greater than the inner diameter of the lower portion of the second pass tube, this alternative may be referred to as "three times diameter-variable";

(5) The inner diameter of the first-pass tube is equal, the inner diameter of the connecting member is larger than the inner diameter of the first-pass tube, and the inner diameter of the lower portion of the second pass tube is larger than the inner diameter of the connecting member. Large, the inner diameter of the upper portion of the second pass tube is greater than the inner diameter of the lower portion of the second pass tube, and this alternative may be referred to as "four times diameter-variable"; And

(6) the inner diameter of the first-pass tube is variable; The inner diameter of the lower portion of the first-pass tube is greater than the inner diameter of the upper portion of the first-pass tube.

According to the diameter-variable arrangement described above, the cross-sectional area of the radiant coil increases as the decomposition process proceeds, so that the pressure drop along the tube length is reduced (the partial pressure of hydrocarbon is reduced), and thus the requirements of the decomposition reaction are better. Is satisfied, high decomposition performance is obtained. Due to the same yield of decomposition products, the decomposition temperature can be lowered, while at the same decomposition temperature, the yield of ethylene product can be effectively improved.

According to a preferred embodiment of the invention, in each group of radiation coils, each first-pass tube is parallel to each other, each second-pass tube is parallel to each other, the first-pass tube and the second The pass tubes are parallel to each other; The plan view of the plane receiving the centerlines of the first-pass tube and the second-pass tube in a plan view is straight; The respective inlet bending tubes are parallel to each other, and their projections in plan view form the same inlet angle with respect to the straight line; Each outlet bending tube is parallel to each other, and their projections in plan view form the same outlet angle with respect to the straight line; The inflow angle is the same as the outflow angle.

According to a preferred embodiment of the invention, in each group of radiation coils, each first-pass tube is parallel to each other, each second-pass tube is parallel to each other, the first-pass tube and the second The pass tubes are parallel to each other; The plan view of the plane receiving the centerlines of the first-pass tube and the second-pass tube in a plan view is straight; The respective inlet bending tubes are not parallel to each other, and their projections in plan view form different inflow angles with respect to the straight line; The respective exit bending tubes are not parallel to each other, and their projections in plan view form different outflow angles with respect to the straight line; For each radiation tube, the inlet angle is the same as the outlet angle.

According to a preferred embodiment of the invention, the radiant coil may comprise one or more tube sections having a twisted baffle therein, the twisted baffle extending inside the tube section along the tube section and the twisted baffle Two spiral passages are formed on both sides of the twisted baffle, which are integrally formed with the tube section.

By providing a twisted baffle inside the radiant coil of the present invention, when the in-process material passes through the surface of the twisted baffle inside the tube section, the twisted baffle causes the in-process material to pass through the tube section. By transferring away from the center and flowing forward in a helical direction rather than straight, the in-process material passing through the interior of the tube section flows laterally while moving forward and is strongly sprayed onto the inner surface of the tube section. In this way, the thickness of the peripheral laminar-flow layer on the inner surface of the tube section (especially a layer with normally high heat resistance, especially when thick) is substantially reduced, so that the heat transfer efficiency is reduced. Is improved. When the heat transfer efficiency is improved, the temperature of the inner wall of the radiation coil is lowered, and thus the coking tendency is suppressed, which further improves the heat transfer efficiency.

According to a preferred embodiment of the invention, the twist angle of the twisted baffle is between 100 and 360 °, the axial length of the tube section is pitch every 180 ° of twist angle of the twisted baffle, The ratio of said pitch to 2 is 3; The thickness of the twisted baffle substantially corresponds to the wall thickness of the tube section; In each cross section of the tube section, the transition zone from the surface of the twisted baffle to the surface of the tube section and vice versa has the shape of a concave arc.

According to a preferred embodiment of the invention, the radiation coil comprises multiple tube sections each having a twisted baffle therein, the multiple tube sections arranged within at least a predetermined length of the radiation coils spaced apart from each other, The distance between two adjacent tube sections is at least 5 pitches. With this kind of arrangement, the total length of all of the tube sections with twisted baffle (s) is only a small fraction of the total length of the radiation coil. Therefore, since the resistance to the material in the flowing process is not substantially increased, the material in the process can be moved forward in helical motion to improve heat transfer efficiency, while at the same time the flow rate in the process is not substantially reduced. .

With the help of the twisted baffle inside the tube section, the material in the process is laterally transported away from the center of the tube section, thereby being strongly sprayed onto the inner surface of the tube section. In this way, the thickness of the surrounding laminar flow layer on the inner surface of the tube section (particularly the layer having normally high heat resistance, especially when thick) is substantially reduced. Thus, the resistance of the tube wall to the material in the process is reduced, so that the speed of progress of the material in the process can be increased appropriately.

As the temperature of the inner wall of the radiation coil in the cracking furnace is lowered, the service life of the radiation coil in the cracking furnace is extended.

For the same reason, by arranging the tube section (s) with twisted baffle (s) in a tubular cracking furnace, heat transfer efficiency can be improved at a relatively low cost, and a larger amount of flowing in-process material decomposes. Can pass through the furnace.

According to a preferred embodiment of the invention, the projection shape of the return bending tube in side view is camber, semi-circular, semi-elliptical or parabolic.

According to a preferred embodiment of the invention, the group of radiant coils may comprise two or more radiant coils, wherein all first-pass tubes and all second-pass tubes in each group of radiant coils are each grouped. (collectively) arranged.

According to a preferred embodiment of the invention, the two groups of second pass tubes of the radiation coil are arranged adjacent to form one module; A plurality of said modules are arranged in the radiation section of the cracking furnace, and the centerlines of the first-pass tubes and the second-pass tubes of each group are in the same plane.

According to a preferred embodiment of the invention, the radiation section of the cracking furnace is arranged with a plurality of groups of radiation tubes, wherein the first group of first pass tubes of the radiation tubes is the second pass of another group of radiation tubes. Arranged adjacent to the tubes, the centerlines of the first-pass tubes and the second-pass tubes of each group are in the same plane.

In the above arrangement, since the projection of each connecting member on the side view is the same curve that is symmetrical, continuous and closed, the deformation of the connecting member is also symmetrical when subjected to heat. Thus, it is possible to ensure that the heating is uniform, and the single-column arrangement can be kept unchanged. Specifically, the two passes furnace tube are in the same plane, the connecting members of the two passes tube are arranged on two sides of the plane, and the center of gravity of the tube is in the plane. On the other hand, the first-pass tube and the second-pass tube are arranged together in a group state, respectively. When the second-pass tube extends in the downward direction, both the connecting member and the first-pass tube move regularly in the same direction, and thus, when operating in a heated state, bending and moving direction differentiation of the tube ( Since the center of gravity of the tube is not in the plane of the tube), further ensuring that the first-pass furnace tube and the second-pass furnace tube are in the center plane of the furnace chamber, thus avoiding uneven heating. The objective is achieved. Thus, furnaces having a furnace tube arrangement of this kind have advantages such as long service life and good mechanical properties.

In each group of radiation coils, each first-pass tube is parallel to each other, each second-pass tube is parallel to each other, and the first-pass tube and second-pass tube are parallel to each other; The projection of the plane receiving the centerlines of the first-pass tube and the second-pass tube on the plan view is a straight line. However, the inlet bending tube and the outlet banding tube can be arranged in several ways. One way is that each inlet bending tube is parallel to each other with a projection in a top view which forms the same inflow angle with respect to the straight line; Each outlet bending tube is parallel to each other with a projection in a plan view forming an equal outflow angle with respect to said straight line; The inflow angle is the same as the outflow angle. Another way is that the respective inlet bending tubes are not parallel to each other with their projections in the top view forming different inlet angles with respect to the straight line; Each outlet bending tube is not parallel to each other with a projection in a plan view forming a different outlet angle with respect to said straight line; The inflow angle is the same as the outflow angle.

According to different requirements, the radiant coils of the group may comprise two or more radiant coils, in which all first-pass tubes and all second-pass tubes in each group of radiant coils are arranged in groups. The radiation section of the cracking furnace is arranged in a plurality of groups of radiation tubes, the arrangement of which may be in several ways, one way in which the second pass tube of the two groups of radiation coils forms a module. Arranged adjacently, the centerlines of the two groups of first-pass tubes and second-pass tubes are in the same plane; A plurality of said modules are arranged in the radiation section of the cracking furnace, and the centerlines of the first-pass tubes and the second-pass tubes of each group are in the same plane. In another manner, the first-pass tube of a group of radiation tubes is arranged adjacent to the second-pass tube of another group of radiation tubes, and the first-pass tube and the second-pass tube of each group are arranged. The centerline of is in the same plane. In such an arrangement, when the arrangement of the tubes has an odd number, the first-pass tube and the second-pass tube can be arranged alternately, so that the heating of the tube in the combustion chamber of the radiation section will be more uniform.

According to practical requirements, twisted baffles can be integrated with the diameter-varying zone of the tube to reduce costs and improve heat transfer effects; Twisted baffles may also be arranged in the non-variable region of the tube. The overall objective is to enhance the diameter-varying effect in order to improve the cracking performance, ie to extend the run length and improve the olefin yield.

In practicing the present invention, the number of groups of radiant coils is related to the capacity of the furnace, which can be determined according to the design conditions such as the feedstock, the capacity of the cracking furnace, the running length and the like.

Generally speaking, compared to the prior art, the present invention provides the following beneficial effects:

(1) Since the radiation coil of the present invention is arranged in a diameter-varying manner, in particular in a continuous multi-diameter-varying manner, the cross section of the radiation coil is increased as the decomposition process proceeds, so that the pressure drop in the tube length is reduced, The requirements of the decomposition reactions are thus better met, resulting in higher decomposition performance. Due to the same yield of decomposition product, the decomposition temperature can be lowered, on the other hand, the yield of the olefin product can be effectively improved at the same decomposition temperature.

(2) In actual operation, the tube wall temperature of the radiation tube decreases. The operation length is extended, and the time for increasing or decreasing the combustion chamber temperature can be shortened. The furnace tube has good mechanical performance and therefore does not bend easily. The service life of the tube can be extended for an additional 2-3 years.

(3) As described above, since the tube section with the internal twisted baffle (s) is provided in the radiation coil of the ethylene cracking furnace of the present invention, the ethylene cracking furnace of the present invention has a relatively good heat transfer efficiency and less coking. Trend, stable and reliable operability, and a longer service life of the device.

1 is a schematic view of a decomposition furnace of the present invention.
2 is a schematic view (front view, side view and top view) of a group illustrating a group of radiation coils in accordance with an embodiment of the present invention.
3 is a schematic view (front view, side view and top view) of a group illustrating a group of radiation coils in accordance with an embodiment of the present invention.
4 is a schematic plan view showing an arrangement of two groups of radiation coils according to an embodiment of the invention.
5 is a schematic plan view showing an arrangement of two groups of radiation coils according to an embodiment of the invention.
6 is a schematic plan view showing an arrangement of two groups of radiation coils according to an embodiment of the invention.
7 is a schematic diagram of a group illustrating a group of radiation coils in accordance with an embodiment of the present invention.
8 is a schematic diagram of a group illustrating a group of radiation coils in accordance with an embodiment of the present invention.
9 is a schematic diagram of a group illustrating a group of radiation coils in accordance with an embodiment of the present invention.
10 is a schematic side view showing a tube section with a twisted baffle according to an embodiment of the invention, with the cross-sectional positions BB, CC and DD indicated.
FIG. 11 is a schematic view of the end as viewed according to arrows A or E of FIG. 10.
12 is a cross-sectional view taken along line BB of FIG. 10.
FIG. 13 is a cross-sectional view taken along line CC of FIG. 10.
14 is a cross-sectional view taken along line DD of FIG. 10.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

As shown in FIG. 1, the ethylene cracking furnace according to the invention comprises a high pressure steam drum 1, a convection section 2, a radiation section 3, a plurality of groups of radiation coils 4 arranged perpendicularly to the radiation section. ), Burner 5 and delivery line exchanger 6.

As shown in FIG. 2, each of the radiation coils has a first pass tube 7, a second pass tube 8, and a connecting member 9 connecting the first pass tube and the second pass tube. It includes; The feedstock is introduced into the inlet end of the first-pass tube 7 and flows out of the outlet end of the second-pass tube 8.

The first-pass tube 7 and the second-pass tube 8 are undivided furnace tubes, the centerline of each furnace tube being in a common plane. The diameters of the first-pass tube 7, the second-pass tube 8, and the connecting member 9 are varied one or more times.

The connecting member (9) comprises an inlet bending tube (10), a return bending tube (11) and an outlet bending tube (12); Each first-pass tube 7 is connected to the end of the inlet bending tube 10 at the end of the first-pass tube 7 remote to the inlet end of the first-pass tube, and the return bending tube. Another end of (11) is connected to the end of the outlet bending tube 12, and the other end of the outlet bending tube 12 is the second-pass tube that is far from the outlet end of the second-pass tube. (8) is connected to the end.

The inlet bending tube (10) and the outlet bending tube (12) are arranged on two sides of a plane which receives centerlines of the first-pass tube (7) and the second-pass tube (8), respectively; The plane formed by the centerline of the group of inlet bending tubes 10 intersects with the plane formed by the centerline of the group of outlet bending tubes 12, the intersection line of which is the first-pass tube 7. And the two planes which are in a plane for receiving the centerline of the second-pass tube 8 and formed by the centerlines of the inlet and outlet bend tubes. Symmetric about the plane that receives the centerline; The return bending tubes 11 connecting the group of inlet bending tubes 10 and the group of outlet bending tubes 12 are parallel to each other, and their projections on the top view are straight lines with the same length; The shape of the return bending tube 11 on the side view is semicircular. The projection of each of the connecting members 9 on the side view is the same curve which is symmetrical, continuous and closed.

In each group of radiation coils, each first pass tube 7 is parallel to each other, each second pass tube 8 is parallel to each other, and the first pass tube 7 and the second pass The tubes 8 are parallel to each other; The projection of the plane receiving the centerlines of the first-pass tube 7 and the second-pass tube 8 on the plan view is a straight line. However, the inlet bending tube 10 and the outlet bending tube 12 can be arranged in various ways.

One way is shown in Fig. 2, wherein each inlet bending tube is parallel to each other and its projection on the top view forms the same inlet angle with respect to the straight line; Each outlet bending tube is parallel to each other and its projection on the top view forms the same outlet angle with respect to the straight line; The inflow angle relative to the outflow angle is preferably 70 °.

Another way is that each inlet bending tube 10 is not parallel to each other and its projection on the top view forms a different inlet angle with respect to the straight line; Each outflow bending tube 12 is not parallel to each other and its projection on the top view forms a different outflow angle with respect to the straight line, the angle of which varies in the range from 65 ° to 90 °, but for each radiation tube The inflow angle is the same as the outflow angle.

According to different requirements, a group of radiation coils may comprise two or more radiation coils, and in each group of radiation coils all first-pass tubes 7 and all second-pass tubes 8 Each is arranged in groups. The radiation section of the cracking furnace is arranged in a plurality of groups of radiation tubes, which arrangement may be in several ways. In one way, the two groups of second pass tubes of the radiation coil are arranged adjacent to form a module, wherein the centerlines of the two groups of first pass and second passes tubes are in the same plane and ; The inlet bending tubes of the first group of connecting members and the inlet bending tubes of the second group of connecting members are arranged on both sides (FIG. 4) or on the same side (FIG. 5) on both sides; A plurality of said modules are arranged in the radiation section of the cracking furnace, and the centerlines of the first-pass tubes 7 and the second-pass tubes 8 of each group are in the same plane. Another way is shown in FIG. 6, where the first-pass tube of a group of radiation tubes is arranged adjacent to the second-pass tube of another group of radiation tubes, and the first-pass tube of each group. The centerlines of the and second-pass tubes are in the same plane.

The radiant coils can be arranged in a diameter-varying manner in order to meet the requirements of lowering the temperature and reducing the pressure drop during the decomposition process while maintaining the heat absorption invariant. For different requirements, the diameter-variable arrangement can be realized by a number of alternatives:

Alternative A : The inner diameter of the first-pass tube 7 is equal to the inner diameter of the connecting member 9 and the inner diameter of the lower portion of the second-pass tube is different from the inner diameter of the connecting member 9. , The inner diameter of the upper portion of the second pass tube 9 is also different from the inner diameter of the lower portion of the second pass tube (FIG. 7);

Alternative B : The inner diameter of the first-pass tube 7 is varied (the inner diameter of the upper portion is different from the inner diameter of the lower portion), and the inner diameter of the connecting member 9 is the lower side of the first-pass tube 7. Same as the inner diameter of the part, and the inner diameter of the second-pass tube 8 is uniform (invariant) (FIG. 8);

Alternative C : The inner diameter of the first-pass tube 7 is varied (the inner diameter of the upper portion is different from the inner diameter of the lower portion), and the inner diameter of the connecting member 9 is the lower side of the first-pass tube 7. The inner diameter of the lower part of the second pass tube 8 is the same as the inner diameter of the part, and the inner diameter of the upper part of the second pass tube 8 is different from that of the second pass. Different from the inner diameter of the lower part of the tube (FIG. 9).

In practicing the present invention, the number of groups of furnace tubes is related to the capacity of the furnace and can be determined according to design conditions such as feedstock, yield of cracking furnace, running length and the like.

The process performance parameters of various embodiments employing 48 radiant coils are as follows:

Comparative Example (Equal Diameter):

Embodiment 1 (Single Diameter-Variable)

Embodiment 2 (Twice Diameter-Variable)

Embodiment 3 (3 times diameter-variable)

10-14, the present invention also provides a tube section 100 with a twisted baffle. From the cross-sectional view shown in FIG. 11, the tube section 100 with twisted baffle according to the invention comprises a tube or flue part 110 and a twisted baffle or turbulator part 120. Able to know. The twisted baffle portion 120 is integrated with the tube portion 110 of the tube section 100. As shown in FIG. 11, the twisted baffle portion 120 extends across the tube portion 110 in the radial direction to allow the in-process cavity to flow through the inner cavity of the tube section 100. Is divided into passages 130 and 140. The passages 130 and 140 have substantially the same cross sectional area.

According to the inventive concept, in all cross sections of the tube section 100, each transition zone, i.e. between the surface of the twisted baffle and the inner wall surface of the tube section 100 in the passages 130 and 140, i.e. The corner portions 150, 160, 170, 180 shown in FIG. 11 are concave arc shaped. Specifically, the radius of the concave arc should not be too long, otherwise the passages 130 and 140 will be too narrow to limit the flow rate of the material in the process. On the other hand, the radius of the concave arc should not be too short, otherwise the material in the process will form eddy, which is likely to start coking at the corners.

The length of the tube section with the twisted baffle shown in FIG. 10 is one pitch. Thus, the end seen in the direction of arrow A is the same as seen in arrow E. FIG. As shown in FIG. 11, the twisted baffle portion 120 is horizontal.

12 is a cross-sectional view of the tube section 100 of FIG. 10 located at a point 1/4 of the total length of the tube section 100 from the left end of the tube section. As shown in FIG. 12, the twisted baffle 120 is in an inclined state with a 45 ° inclination angle to the upper left direction.

FIG. 13 is a cross-sectional view of the tube section 100 of FIG. 10 located at a point half the total length of the tube section 100 from the left end of the tube section. As shown in FIG. 13, the twisted baffle 120 is in a vertical state.

FIG. 14 is a cross-sectional view of the tube section 100 of FIG. 10 located at a point three quarters of the total length of the tube section 100 from the left end of the tube section. As shown in FIG. 14, the twisted baffle 120 is in an inclined state with a 45 ° tilt angle upwards in the right direction.

In a word, in the present invention, the geometry and dimensions of all axial cross sections of the tube section 100 are always the same, except that the twisted baffle portion 120 has a different angle of inclination. The three-dimensional shape of the twisted baffle portion 120 can be drawn through FIGS. 10 to 14.

In fact, the twisted baffle portion 120 can be twisted in both the left and right directions.

The twisted baffle portion 120 may be arranged in the radial direction or in the non-diameter direction (off the radial direction). When arranged in the non-diameter direction, the passages 130 and 140 will have different cross-sectional areas.

The cross section of the twisted baffle portion 120 may be straight (as shown in FIGS. 10-14) or curved (not shown).

Depending on the practical requirements, the twisted baffle portion 120 can be designed to have a more complex shape such that the tube section divides the inner cavity of the tube section into more than two passageways for the flow of material in the process.

In the present invention, the term "pitch" (S) means the axial length of the tube section at all twist angles 180 ° of the twisted baffle. The term " twisted ratio " (Y) means the ratio of the pitch S and the inner diameter D of the tube section, ie Y = S / D.

Thus, the smaller the value of Y, the higher the twist angle of the twisted baffle. Therefore, the in-process material in the tube section tends to flow laterally, the heat transfer efficiency is better, and the coking tendency is better reduced. However, if the value of Y is too small, the resistance to the flow of the material in the process is greatly increased, thereby limiting the flow rate of the material in the process.

On the other hand, the larger the value of Y, the lower the twist angle of the twisted baffle. Thus, the tendency of the in-process material in the tube section to flow laterally is lower, and the resistance to the flow of the in-process material is reduced, thereby improving the flow rate of the in-process material. However, the heat transfer efficiency is reduced, so that the tendency to coke is reduced.

Therefore, it is important to determine a suitable distortion ratio. In the present invention, Y = 2.5 can realize a perfectly good effect; When Y is selected in the range of 2 to 3, the device will work very well.

If a tube section with twisted baffles is provided axially throughout the length of the furnace tube, the heat transfer efficiency can be greatly increased. However, the resistance to the flow of the material in process will also be greatly increased, so the flow rate will be reduced. For this reason, in the present invention, the tube section with the twisted baffle is arranged only in a few places of the furnace tube, and two adjacent tube sections with the twisted baffle have a predetermined length (empty tube section) without the twisted baffle. Are separated from each other by Since the material in process has a helical inertia force when exiting a tube section with twisted baffles, the material in process can still flow forward while helically moving within the empty tube section.

The spacing between two adjacent tube sections with twisted baffles may be set at least 5 pitches. According to some preferred embodiments, the spacing may be 15-20 pitch.

From Table 5 we can see that:

When twisted baffles are added, each characteristic is better, except that the pressure drop is slightly increased.

The more frequent the frequency-change, the better the property.

1: high pressure steam drum, 2: convection section, 3: radiation section, 4: radiation coil, 5: burner, 6: transfer line exchanger, 7: first-pass tube, 8: second-pass tube, 9: connection Member, 10: inlet bending tube, 11: return bending tube, 12: outlet bending tube, 100: tube section, 110: tube portion, 120: baffle portion, 130, 140: passage, 150, 160, 170, 180: corner part

Claims (10)

Ethylene cracking furnace comprising a high pressure steam drum, a convection section, a radiant section, a plurality of groups of radiant coils, burners and transfer line exchangers arranged perpendicular to the firebox of the radiant section. as a cracking furnace,
Each of the radiation coils includes a first-pass tube, a second-pass tube, and a connection member connecting the first-pass tube and the second-pass tube; Feedstock is introduced into the inlet end of the first-pass tube and exits from the outlet end of the second-pass tube;
The first-pass tube and the second-pass tube are non-split radiation tubes, the centerline of each radiation tube being in a common plane;
The connecting member is a three-dimensional structural member comprising an inlet bending tube, a return bending tube and an outlet bending tube; Each first-pass tube is connected to an end of the inlet bending tube at the bottom end of the first-pass tube remote to the inlet end of the first-pass tube, The other end is connected to an end of the return bending tube, the other end of the return bending tube is connected to an end of the outlet bending tube, and the other end of the outlet bending tube is a second-pass tube. Is connected to the bottom end of the second-pass tube that is far from the outlet end of the second pass tube;
The inlet bending tube and the outlet bending tube are respectively arranged on two sides of a plane which receives the centerlines of the first-pass tube and the second-pass tube; The plane formed by the centerline of the inlet bending tube of the group crosses the plane formed by the centerline of the outlet bending tube of the group, and the intersecting line is the centerline of the first-pass tube and the second-pass tube. Wherein the two planes, which are in a plane that accommodates the center line of the inlet bending tube and the outlet bending tube, are symmetrical with respect to the plane that receives the centerlines of the first-pass tube and the second-pass tube; The return bending tubes connecting the inlet bending tube of the group and the outlet bending tube of the group are parallel to each other, and their projections on the plan view are straight lines with the same length; The projection of each connecting member on the side view is the same curve which is symmetrical, continuous and closed,
The inner diameter of the radiation coil is selected from the group consisting of the following alternatives, ethylene cracking furnace:
(1) The inner diameter of the first-pass tube is the same as the inner diameter of the connecting member, and the inner diameter of the second-pass tube is different from the inner diameter of the first-pass tube and the connecting member, and the second An inner diameter of the pass tube is larger than an inner diameter of the first-pass tube and the connecting member;
(2) The inner diameter of the first-pass tube is the same as the inner diameter of the connecting member, and the inner diameter of the lower portion of the second-pass tube is the same as the inner diameter of the first-pass tube and the connecting member, The inner diameter of the upper portion of the second pass tube is greater than the inner diameter of the lower portion of the second pass tube;
(3) the inner diameter of the first-pass tube is equal, the inner diameter of the connecting member is larger than the inner diameter of the first-pass tube, and the inner diameter of the second-pass tube is the same as the inner diameter of the connecting member;
(4) The inner diameter of the first-pass tube is equal, the inner diameter of the connecting member is larger than the inner diameter of the first-pass tube, and the inner diameter of the lower portion of the second pass tube is equal to the inner diameter of the connecting member. The inner diameter of the upper portion of the second pass tube is greater than the inner diameter of the lower portion of the second pass tube;
(5) The inner diameter of the first-pass tube is equal, the inner diameter of the connecting member is larger than the inner diameter of the first-pass tube, and the inner diameter of the lower portion of the second pass tube is larger than the inner diameter of the connecting member. A large, inner diameter of an upper portion of the second pass tube is greater than an inner diameter of a lower portion of the second pass tube; And
(6) the inner diameter of the first-pass tube is variable; The inner diameter of the lower portion of the first-pass tube is greater than the inner diameter of the upper portion of the first-pass tube. The method of claim 1,
In each group of radiation coils, each of the first-pass tubes are parallel to each other, each of the second-pass tubes are parallel to each other, and the first-pass tube and the second-pass tube are parallel to each other. and; The projection of the plane receiving the centerlines of the first-pass tube and the second-pass tube in a plan view is straight; The respective inlet bending tubes are parallel to each other, and their projections in plan view form the same inlet angle with respect to the straight line; Each outlet bending tube is parallel to each other, and their projections in plan view form the same outlet angle with respect to the straight line; The inlet angle is ethylene decomposition furnace, characterized in that the same as the outlet angle. The method of claim 1,
In each group of radiation coils, each of the first-pass tubes are parallel to each other, each of the second-pass tubes are parallel to each other, and the first-pass tube and the second-pass tube are parallel to each other. and; The plan view of the plane receiving the centerlines of the first-pass tube and the second-pass tube in a plan view is straight; The respective inlet bending tubes are not parallel to each other, and their projections in plan view form different inflow angles with respect to the straight line; The respective exit bending tubes are not parallel to each other, and their projections in plan view form different outflow angles with respect to the straight line; In each radiation tube, the inlet angle is equal to the outlet angle. 4. The method according to any one of claims 1 to 3,
The radiation coil comprises at least one tube section having a twisted baffle therein, the twisted baffle extending inside the tube section along the tube section to form two spiral passages on either side of the twisted baffle, The twisted baffle is integrally formed with the tube section. The method of claim 4, wherein
The twist angle of the twisted baffle is 100-360 °, the axial length of the tube section is one pitch for every 180 ° twist angle of the twisted baffle, and the ratio of the pitch to the inner diameter of the tube section is 2 To 3; The thickness of the twisted baffle substantially corresponds to the wall thickness of the tube section; In each cross section of the tube section, the transition section from the surface of the twisted baffle to the surface of the tube section and vice versa have the shape of a concave circular arc. The method of claim 5,
The radiation coils comprise a plurality of tube sections each having a twisted baffle therein, the plurality of tube sections arranged in at least a predetermined length of the radiation coils spaced apart from each other, the distance between two adjacent tube sections being 5 Ethylene decomposition furnace characterized by more than a pitch. The method of claim 1,
In side view, the projection shape of the return bending tube is ethylene cracking furnace, characterized in that the camber, semicircle, semi-ellipse or parabolic. The method of claim 1,
The radiant coils of the group may comprise two or more radiant coils, wherein all the first-pass tubes and all the second-pass tubes in each group of the radiant coils are arranged collectively, respectively. Ethylene decomposition furnace characterized in that. The method of claim 1,
The second-pass tubes of the two groups of radiation coils are arranged adjacent to form one module; And a plurality of said modules are arranged in a combustion chamber of a cracking furnace, wherein centerlines of said first-pass tube and said second-pass tube in each of said groups are in the same plane. The method of claim 1,
A plurality of groups of radiation tubes are arranged in the combustion chamber of the cracking furnace, and the first-pass tube of the group of radiation tubes is adjacent to the second-pass tube of the other group of radiation tubes And the centerlines of the first-pass tubes and the second-pass tubes of each group are in the same plane.

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